The present invention relates to an improvement in a system for driving a plurality of liquid crystal display units each having a common electrode, a plurality of segment electrodes and a liquid crystal composition interposed between the said electrodes.
The liquid crystal display units have been adopted for display units in electronic apparatus such as calculators and watches, since the liquid crystal display units can be driven with less power consumption by a power source of a relatively low level and can indicate patterns of large size on a panel.
The conventional liquid crystal dynamic drive system required four kinds of power sources providing first, second, third and fourth voltage levels with respect to a reference level. The common electrode was connected to receive alternating signals bearing the reference level and the fourth level which are symmetrical to each other with respect to the second level, whereas the segment electrodes were connected to receive alternating signals bearing the first level and the third level. Such a liquid crystal dynamic drive system are described in copending application, DRIVE SYSTEM FOR LIQUID CRYSTAL DISPLAY UNITS, Ser. No. 398,850, filed Sept. 19, 1973 by Isamu Washizuka and assigned to the same assignee as the present application, which is now U.S. Pat. No. 3,902,169.
Recently, CMOS's (complementary metal-oxide-semiconductor) have been used in electronic calculators, since the CMOS's consume less energy and require a lower power source. When the conventional dynamic drive system is applied to an electronic calculator comprising a CMOS-LSI including a computation circuit and storage, and liquid crystal display units containing a liquid crystal composition which generally has a given threshold voltage of 18V, it is necessary to provide an amplifier in order to activate the liquid crystal display units since the voltage difference between the reference level and the fourth level must be more than 24V which can not be endured by the CMOS's. Therefore, a liquid crystal drive circuit can not be included within the CMOSLSI. This may cause increase of the cost for fabricating the electronic calculator and increase of power consumption.